(a) Field of the Invention
The present invention relates a modulation apparatus, a modulation method, a demodulation apparatus, and a demodulation method.
(b) Description of the Related Art
Generally, in a wireless communication system, power consumption has a huge effect on characteristics of a power amplifier, which necessitates a power amplifier that has high power efficiency while improving frequency efficiency and efficient modulation and demodulation methods for the power amplifier.
A non-linear modulation method such as on-off keying (OOK) may use a non-linear power amplifier having high power efficiency.
Meanwhile, when a linear modulation method such as phase shift keying or quadrature amplitude modulation (QAM) that has high frequency efficiency uses a non-linear power amplifier having high power efficiency, the performance of the linear modulation method is degraded.
Therefore, the PSK or QAM method with high frequency efficiency should use a linear power amplifier, thereby increasing power consumption of a transmitting apparatus.
Research on using a non-linear power amplifier with high power efficiency in the linear and non-linear modulation methods has been undertaken to reduce the power consumption of the transmitting apparatus, and the research may be classified into two approaches.
The first approach is to compensate distortion of a signal caused by non-linear characteristics by processing an input signal or output signal of a non-linear power amplifier. The first approach should constitute complex compensation circuits in the front or rear of the non-linear amplifier, thereby increasing complexity of a wireless communication system and the cost for embodying the first approach.
The second approach uses a linear power amplifier and controls bias voltage thereof in order to reduce power consumption. The second approach can reduce the cost for embodying the second approach, and thus research for controlling the bias voltage of the linear power amplifier is now in progress.
According to the progress in controlling the bias voltage of the linear power amplifier, the relation between an instant envelope curve of the signal input to the linear power amplifier and the power consumption is considered important.
From this point of view, a modulation method including a silence signal such as a pulse position modulation (PPM) or bi-orthogonal PPM (BPPM) is considered to have an advantage in reducing the power consumption of the linear power amplifier. The PPM or BPPM method, however, has a silence signal duration, thereby making the frequency efficiency low.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.